I’m seeing this kind of late but have expireince in JL-8 set ups....excessive Axel play will cause piston knock back and a spongy brake pedal. Toms differentials in Idaho had different thickness C-clips for 12 boot axels. You could also have Toms run is a set of posi clutches to minimize later wear....Penske Trans Am cars used the 22 plate posi clutch packs Toms at one time had these too....the 22 plate packs aren’t as “grainy” on the clutch plate surfaces as the 18plate clutch packs are....much smoother. Breaking in the posi clutch pack is done by running on a stationary test fixture or running vehicle in on by doing figure “8’s” in a parking lot. The intial clutch pack wear is considerable can cause a 0.010”-0.040” additional slack in C clip clearances.....the material is really hard and abrasive in nature too coming off the clutch pack plates.....NASTY stuff. I also was told by a good friend who was a mechanic way back when that a SF Bay Area Chevy dealer once warranty swapped a drum braked 12 bolt into a JL-8 Camaro as a solution to the spongy brake pedal syndrome in a street driven Z/28....way back when. 0.005” should be considered a max figure in axle endplay when building a JL/8 12 bolt with a broken in posi clutch pack. After initial break in the clutch pack wear is substantially reduced. I hope you know not to run the daisy petal type clutch socks as they can crack and fail in use...GM went to these in the early 70’s to stop warranty complaints of differential chatter in the solid plate clutch packs. I’m not a fan of the O ring style caliper piston seals but if you have end play and soft pedal problems they might assist in reducing aeration problems but again I’m no fan of O ting caliper Pistons.
